Krish
RF STAFF
Hey Tony! You are right about bio-balls as they do produce a lot of nitrates. How your sump is set up doesn't look like if bio-balls were used, that it was in a wet/dry environment, but fully submerged which is a little different. Nevertheless, you don't need them. About your skimmer, most people do have them in their first chamber so it can recieve the water coming in directly from the tank, but in any event, your skimmer will still get a shot at the same in-coming water wherever you put it in the sump as all the water still has to pass throung the entire sump to return back to the tank. So, hanging the skimmer on the return chamber won't defeat it's purpose. IMO, it should still work the same. I only have mine in the first because I use to use a filter pad in my sump and I wanted the skimmer to remove as much junk as possible before the water got to the filter pad so I wouldn't have to worry about cleaning it so much, but I've pretty much done away with every pad/sponge all together in my system except for on my prefilter. HTH and good luck!